1. Field of the invention
The present invention relates to cylinder block structure and particularly to cylinder block structure which forms a cooling water passage so as to introduce cooling water into the inside by inserting a hollow member having arc guide pieces into the upper end between the cylinder bores and thereby cools the upper ends of cylinder bores uniformly and minimizes thermal distortion of those parts for improvement of its durability in the Siamese type cylinder block.
2. Description of the prior art
The usual Siamese type cylinder block is a cylinder block which minimizes its length by minimizing a space between the cylinder bores to reduce its weight.
In said cylinder block, there is no cooling water passage formed between the cylinder bores adjoining each other. So, if the cylinder block is heated by the heat inevitably generated when the engine operates, it is apt to be distorted by a disparity of thermal expansion between a space portion of cylinder bores without a cooling water passage and an external portion of cylinder bores with a cooling water passage. If cylinder bores are thereby distorted, the piston ring united with the upper side of the piston which reciprocates upward and downward within the cylinder does not uniformly seal to the cylinder wall but partially stick thereto, and loosely adhering phenomenon is thereby presented between them.
Moreover, in casting a Siamese type cylinder block, there is no sand supported between the cylinder bores in the water jacket core by a sand mold. So its rigidity is apt to be weakened and damaged. When cast, it is distorted so that the wall thickness bore cannot be of precise.
In order to solve such problems as stated hereinabove, various methods for improving cooling effects by froming a cooling water passage between the cylinder bores so as to enable cooling water to pass therethrough have been suggested.
One form of those conventional cylinder block structures is a method in which a cooling water passage is formed between the cylinder bores by using a ceramic core. The method for casting a cylinder block by interposing an expensive ceramic core between the neighboring cylinder bores when a cast cylinder block is manufactured and forming a cooling water passage communicating with the left and right water jackets between the cylinder bores is known.
However, this method involves a problem in that it is uneconomical because the ceramic core itself is very expensive and that it is difficult to insert and fix the ceramic core when a cylinder block is founded.
Another method is a method in which a cooling water passage is formed between the cylinder bores by giving a slope thereto with a drill, as described in the U.S. Pat. No. 4,369,739. The method for forming a cooling water passage with a drill at an incline of 20-30 degrees from the upper part of cylinder block after casting is completed is known.
However, such a method meets a problem in that drilling work is not only difficult and complicated but also uneconomical because drills are cut damaged so often and that the cooling water passage is unable to serve as such when a cut damaged drill gets caught in the cylinder block.
Although the method for forming a cooling water passage between the cylinder bores of a molded cylinder block with a side cutter is known, it still runs into a problem in that forming of the cooling water passage by processing a molded cylinder block with a separate side cutter requires so greater care that work efficiency lowers.
The U.S. Pat. No. 4,470,376 discloses a cylinder block wherein a cooling water passage is formed by inserting a reinforced plate member with a number of openings formed between the cylinder bores and linking it to the outer walls of water jackets, but it encounters a problem in that it is liable to move when cast because its uniting rigidity with the water jacket core is not so solid.
Another conventional art uses a steel bar to keep the water jacket core from being distorted in the Siamese type cylinder block. Although a steel bar with both ends bending upward is inserted between the bores of water jacket core when it is molded with the water jacket core, it is apt to move when high-pressure sand is injected in the process of manufacturing a water jacket core. Moreover, a steel plate is inserted between the bores of water jacket core when a water jacket core is molded, but it is liable to move when the water jacket core is manufactured because its uniting rigidity with the water jacket is not so solid, and the sand weakly united with the steel bar or steel plate is separated therefrom when cast and disturbs the flow of cooling water by being united with melted iron.
According to those methods described hereinabove, a cylinder block is cast by using a separate core and then the core must be taken out or a cooling water passage must be formed with a separate implement after a cylinder block is cast. Consequently, those methods are uneconomical not only for the reason that durability of the cylinder block is weakened and inferior cylinder blocks are produced in many cases but also for the reason that the cooling water passage is not precise, and so manpower and time are wasted to a considerable degree. Moreover, use of an expensive core raises manufacturing cost.